1. Field of the Invention
The present disclosure generally relates to reservoir sampling and testing and in particular to methods and apparatus for estimating properties of downhole fluids.
2. Description of the Related Art
Oil and gas wells have been drilled at depths ranging from a few thousand feet to as deep as five miles. A large portion of the current drilling activity involves directional drilling that includes drilling boreholes deviated from vertical by a few degrees to horizontal boreholes, to increase the hydrocarbon production from earth formations.
Information about the subterranean formations traversed by the borehole may be obtained by any number of techniques. Techniques used to obtain formation information include obtaining one or more core samples of the subterranean formations and obtaining fluid samples produced from the subterranean formations these samplings are collectively referred to herein as formation sampling.
Exploration, drilling and production operations are facilitated by gathering various types of downhole information relating to the operation of a drill string, wireline or slick line within a borehole; relating to components of downhole tools; relating to downhole fluids including drilling fluid, return fluid and formation fluid; and/or relating to formation samples, formation fluid within the formation and the formation structure.
Some such operations for collecting information downhole make use of optical sensors. Unfortunately, such sensors typically include fragile components and may not perform well in a downhole environment. Examples include various embodiments of interferometers.
In some embodiments of interferometers for downhole measurements, aspects such as a light source, interferometer, and associated photodetectors are maintained topside (above ground) in order to avoid the detrimental performance realized downhole, which leaves only the fiber cable and fiber optic sensor downhole. Of course, it is easily recognized that having an instrument with various components downhole and others topside presents many limitations including requiring a fiber optic cable from the surface to downhole, which is not practical while a drill string is drilling in the well. Having far separated components affects the versatility of drilling or logging equipment downhole.
Accordingly, what are needed are methods and apparatus for providing a robust interferometer downhole. Preferably, the apparatus are compact and physically robust, such that limitations are not imposed on other uses of downhole tooling and reliable data can be collected.